Mesa County prosecutors say an 18-year-old man was plotting a "profoundly disturbing" attack on his high school with weapons and explosives.

Authorities are holding 18-year-old Robert Dell Johnson on $100,000 bail on charges of criminal solicitation and interference with an education institution. More charges expected.

District Attorney Pete Hautzinger revealed few specifics on the investigation of the threat against Palisade High School but the sheriff said it was credible.

Deputies arrested Johnson Monday night at his home.

One of Johnson's relatives described him as "a young man talking in anger and with nothing to back it up."

Johnson's attorney, Matthew Sandler, did not immediately return a call.

He is scheduled in court for formal filing of charges on Oct. 8.